The present invention is related to a stepless transmission using a friction disc which allows cost reduction of the device by simply forming a cam to press a friction disc.
Hitherto there is known a stepless transmission having a speed changing system which uses a pair of discs and shifts by changing the contacting position of both the discs.
Such a transmission, as schematically shown in FIG. 6, is equipped with a friction disc a on the output side facing toward a rotary disc b which rotates while having a slight inclination against the center line of rotation of the friction disc to input side, wherein torque is transmitted from input side to output side by pressing to connect the friction disc a with the rotary disc b, and by moving the rotary disc b while keeping it pressed and connected with the friction disc, the pressure-connecting position is dislocated, resulting in speed change.
Thus, the friction disc a rotates having the same center with an output shaft and being kept pressed against the rotary disc b while.
Furthermore, in order to press the friction disc a, a cam d which moves along the shaft center of the output shaft c and a spring e which thrusts the friction disc a toward the rotary disc b are employed.
As the cam d is to generate a contacting pressure between the friction disc a and the rotary disc b in proportion to transmission torque, the cam face should be formed with relatively high precision.
However, in order to precisely couple the cam face positioned on output shaft c side and the driven face positioned in friction disc a side, both the cam face and the driven face have had curved surfaces such as spiral surfaces, and the curved surfaces have been formed by a machining process using, for example, a milling machine. Such a machining process needs time and high production cost which results in increased cost of the device.
The present inventor, as a result of studying hard to solve these problems, has found that a laser beam can be adapted to form a cam face, and that by employing a cam formed by laser beam in a stepless transmission, the device works smoothly with the cam.
The object of the present invention is to provide a stepless transmission that improves precision of the coupling and reduces cost, basically by forming a cam face of a driven face cut off by a laser process which couples with a cam face.
In order to solve the problems, the stepless transmission of this invention comprises:
an output shaft equipped with a cam which contains an outward output shaft part and an inward cam face;
a tabular sleeve with a driven face into which the output shaft is inserted so as to be movable along the center line of rotation of the output shaft by a relative rotation of the driven face and the cam face;
a friction disc which is fixed on the sleeve; and
a rotary disc which is pressed to contact the friction disc and moves relatively to the friction disc; wherein
the cam face or the driven face is formed by cutting off by means of laser process.
Moreover, in the stepless transmission of this invention, the cam and the sleeve are cut off and formed by means of laser process from a tubular form, and the cut section of the cam side forms the cam face and the cut section of the sleeve side forms the driven face.
As the cam face or the driven face is cut off and formed by a laser process, even in the case where the cam face or the driven face is formed in complex curved surfaces such as spiral surfaces, it can be formed precisely and easily.
Thus, the sleeve can be pressed against the rotary disc in proportion to transmission torque, and as for the contacting pressure between the friction disc and the rotary disc, it is enough for the stepless transmission to give nearly a minimum necessary pressure that matches with the output torque, which helps to improve durability of the device. In addition, even when the friction disc is worn and reduced in thickness, the sleeve moves inward, thereby transmitting torque without any problem. Moreover, by adopting a laser process, necessary time for processing the cam face or driven face can be dramatically shortened as compared with the conventional machine cutting process, which leads to reduced cost of the devices.